1. Field of the Invention
The present invention relates to an induction heating cooker and a method for operating the same, and more particularly to an induction heating cooker which includes a container material discriminating unit capable of accurately discriminating whether the material of a cooking container placed in the induction heating cooker is magnetic or non-magnetic, based on a phase change in a resonant capacitor voltage of an inverter circuit caused by a difference between resonance characteristics of a magnetic load and resonance characteristics of a non-magnetic load, and a method for operating the induction heating cooker.
2. Description of the Related Art
An example of a conventional induction heating cooker is illustrated. The configuration of the conventional induction heating cooker and problems incurred therein will be described below with reference to FIG. 1. FIG. 1 is a block diagram illustrating configurations of an inverter circuit and a container material discriminating unit included in the conventional induction heating cooker.
The induction heating cooker includes an inverter circuit for generating a magnetic field by causing current to flow through a coil in accordance with a switching operation of a switch element, and inducing the magnetic field into a cooking container placed in the induction heating cooker, thereby generating eddy current to heat the cooking container.
The inverter circuit includes an AC power source adapted to supply a general AC voltage, a rectifier adapted to rectify the AC voltage supplied from the AC power source, a filter adapted to filter the rectified voltage outputted from the rectifier, and a switching unit adapted to perform a switching operation in response to the filtered voltage outputted from the filter, thereby applying a high-power, high-frequency voltage to the coil.
Such a conventional induction heating cooker also includes a container material discriminating unit. This container material discriminating unit will be described in detail with reference to FIG. 1. The container material discriminating unit includes a current detecting unit 1 adapted to detect current flowing through the coil of the inverter circuit, and a voltage comparing unit 2 adapted to compare a DC voltage outputted from the current detecting unit 1 with a reference voltage, which is a divided voltage obtained by two resistors.
The current detecting unit 1 includes a current detector, a diode, and a capacitor. The current detector detects high-frequency sine wave current components from current flowing through the coil of the inverter circuit. The detected current is rectified and smoothed by the diode and capacitor, so that a DC voltage is outputted from the current detecting unit 1.
The DC voltage outputted from the current detecting unit 1 is inputted to the voltage comparing unit 2. In the voltage level comparing unit 2, the DC voltage is compared with a reference voltage, which has a predetermined voltage level for discrimination of a magnetic or non-magnetic load. When the DC voltage is less than the reference voltage, the voltage comparing unit 2 determines that the cooking container is a magnetic load, and generates a corresponding discrimination signal. On the other hand, when the DC voltage is more than the reference voltage, the voltage comparing unit 2 determines that the cooking container is a non-magnetic load, and generates a corresponding discrimination signal.
The discrimination signal generated from the voltage comparing unit 2 is applied to a microcomputer 3. When the microcomputer 3 determines, based on the discrimination signal, that the cooking container is a magnetic load, it activates the inverter circuit to heat the cooking container. On the other hand, when the microcomputer 3 determines that the cooking container is a non-magnetic load, it does not activate the inverter circuit, and controls the cooker to operate appropriately.
However, the above-mentioned conventional container material discriminating unit has problems. For example, when the DC voltage indicative of the value of the current detected by the current detecting unit 1 has a level equal to or approximate to the reference voltage, the voltage comparing unit 2, which discriminates the material of the cooking container, may operate erroneously. In this case, the induction heating cooker may operate erroneously.
In order to detect the high-frequency coil current generated from the inverter circuit, it is necessary to use an expensive current detector, which is made of a ferrite material. For this reason, there is an increase in manufacturing costs.